1. Field of the Invention
The present invention relates to a method of forming a semiconductor boule, and more particularly to a method of forming a semiconductor boule compound by a direct synthesis.
2. Description of the Related Art
A conventional method of forming a III-V semiconductor compound, such as a gallium arsenide (GaAs) boule, utilizes gallium (Ga) and arsenic (As) as starting materials and B.sub.2 O.sub.3 as a liquid encapsulant. These materials are charged into a crucible and melted. The starting materials of gallium and arsenic, are directly synthesized in the crucible to make a GaAs boule.
The GaAs boule formed by this method is usually used for a substrate on which an electric device, such as a Hall sensor or a high frequency FET may be formed.
In a conventional method of manufacturing such electric device, using the GaAs substrate formed by direct synthesis, there is a problem in that the deviation among production lots becomes unacceptably large, and the yield of products (electric devices) deteriorates. This results in large deviations of characteristics among devices manufactured. It is believed that the deviations in characteristics are caused by deviations in the composition of the melt during the manufacture of the GaAs boule, resulting from an evaporation loss of arsenic during manufacture of the boule.
No practical method to suppress the deviations in the composition of the melt previously has been found. In other semiconductor boule compounds, for example, AlAs, InAs and GaSb, similar problem as with the GaAs boule has occurred.
Accordingly, a method for manufacturing semiconductor boule compound is desired in which deviations of the composition of the melt are reduced and a high quality boule is obtained.
An object of the invention is to provide a method of manufacturing a boule of semiconductor compound which can suppress deviations of composition of melt and obtain a high quality of boule. Additional objects and advantages of the invention will be apparent from the description which follows, or may be learned by practice of the invention.